The present invention relates to a scroll compressor employed as an air compressor, refrigerant compressor, or the like having an improved sealing arrangement.
FIGS. 1A to 1D show the basic components of a scroll compressor. In these drawings, reference numeral 1 designates a fixed scroll, 2 an orbiting scroll, 3 a discharge port, 4 compression chambers, 0 a fixed point on the fixed scroll 1, and 0' a fixed point on the orbiting scroll 2. The fixed scroll 1 and the orbiting scroll 2 are constituted by wraps of complementary (mirror-image) shapes, such as complementary involutes or the like.
The operation of the scroll compressor will next be described. In FIGS. 1A to 1D, the fixed scroll 1 is fixed in position relative to an external frame. The orbiting scroll 2 combined with the fixed scroll 1 as shown in the drawing, is moved in an orbiting pattern relative to the fixed scroll 1. Orbital positions at angles of 0.degree., 90.degree., 180.degree. and 270.degree. are shown in FIGS. 1A, 1B, 1C and 1D, respectively. The attitude of the orbiting scroll does not change with respect to the fixed scroll. As the scroll 2 undergoes its orbiting movement, the crescent-shaped compression chambers 4 gradually decrease in volume so that a fluid which has been taken into the compression chamber 4 at the beginning of the cycle is compressed and discharged through the discharge port 3. During this period, the distance between the fixed points 0 and 0' is constant, that is, EQU 00'=p/2-t,
where p and t respectively represent the pitch of the two wraps and the thickness of each wrap.
In the scroll compressor described above, the seal used at a scroll-side end plate surface significantly affects the compression efficiency because of its length. Although various types of axial seals have been proposed, a tip seal is the most widely used because of its capability to compensate for increases in gap length due to thermal deformation. Such a seal is disclosed, for example, in U.S. Pat. No. 801,182, issued in 1905, Japanese Laid-Open Patent Application No. 117304/1976, and Japanese Published Patent Application No. 28240/1982.
U.S. Pat. No. 801,182 discloses a seal in which sealing material is inserted in a groove formed in an end surface of a scroll-side plate, extending along the spiral wrap. The seal material is urged outwardly by a spring in the axial direction to achieve sealing in the axial direction.
Japanese Laid-Open Patent Application No. 117304/1976 discloses a seal in which the width of a groove formed in an end surface of a scroll-side plate is made larger than that of a seal member and a high pressure fluid flows into the groove through a gap formed between the groove wall and the seal member so that the seal member is urged axially outwardly.
Further, Japanese Published Patent Application No. 28240/1982 discloses a seal in which a groove formed in an end surface of a scroll-side plate opens at one end into a high pressure region at the center portion of the spiral and a seal member inserted into the groove is urged axially outwardly by a high pressure fluid flowing into the groove through an opening formed at one end of the groove.
In the various kinds of tip seals described above, the use of a high pressure sealing fluid has a drawback in that the sealing fluid is apt to leak into the low pressure side of the compression chamber through the gap between the groove and the seal member. Compression losses due to such leakage cannot be disregarded. Further, due to a pressure gradient between the center portion and the outer peripheral portions of the spiral wraps, abrasion is likely to occur in the seal member in regions where the pressing force is strong and leakage in regions where the pressing force is weak. On the other hand, the structure using a spring to achieve sealing is complicated, leading to difficulties in the assembly of such a device.